A) You have disabled folder tasks. Change this in your folder settings (not at home, so i don't recall exactly where to change it). The easiest way to tell, right click on a folder and see if you have the option to customize the folder. If so, under customize, change the settings of the folder to video.

B) Xing has been set as the default player for mpg/mpeg and does not support thumbnail view (I'm guessing here). Change the default player settings back to WMP.